Associated with increasingly higher performances of computers, a demand for higher performances of inputs and outputs also increases, and thus high speed input and output interfaces, such as PCI (peripheral component interconnect) Express, are utilized.
In general, PCI Express is a standard for an interface connecting a CPU (central processing unit) to a peripheral device inside a computer, while an approach to extend to outside a computer is also utilized in recent years. PCI Express connects input/output devices in Point-to-Point fashion, so that it is difficult to connect a plurality of input/output devices by extending a single bus as a PCI bus. Therefore, it is carried out to connect a single PCI Express link extended from a computer main body with a PCI Express switch to connect this PCI Express switch to a plurality of input/output devices.
Since PCI Express is originally a standard for an interface used inside a computer, devices connected over PCI Express often use an identical power supply. Accordingly, in a case of replacing a PCI Express switch or an input/output device set outside a computer, a power supply of the computer itself is often stopped. Since turning off and on the power supply greatly influences systems and services, it is difficult to replace an I/O (input/output) expansion box in association with turning off and on the power supply in a current situation.
Therefore, there is a technique of providing redundancy for a switch that connects a plurality of host computers to PCI Express slots to have input/output devices installed therein to suppress stopping of systems and services when the switch fails. There is also HotPlug allowing to plug and unplug an input/output device while powered on. HotPlug includes processing of HotRemove and HotAdd. HotRemove is to disable a target input/output device to turn off the power supply for the PCI Express slot to be connected to the target input/output device. HotAdd is to turn on, when a new input/output device is inserted into a PCI Express slot, the power supply for the target slot to execute initialization of the input/output device.
Such techniques in the past are found in, for example, Japanese Laid-open Patent Publication No. 2007-280237 and Japanese Laid-open Patent Publication No. 2008-46722.